Soft corals form aragonite-precipitated columnar spiculite in mesophotic reefs.

Surveys conducted in Eilat's upper mesophotic coral ecosystem (MCE) revealed protruding columnar calcareous structures with a Sinularia octocoral colony growing atop of each. The current study addressed the hypothesis that these colonies produce spiculites, and sought to determine (a) the spatial occurrence and dimensions of the spiculite-forming colonies and their species affiliation; (b) their microstructural features; and (c) the elemental composition of the columnar spiculites in comparison to the sclerites of the colonies. All the spiculite-forming colonies were exclusively found in the upper MCEs and produced by S. vrijmoethi. This type of spiculite, including its elemental analysis, is reported here for the first time for coral reefs in general and for the MCE in particular. Examination of the spiculites by scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed spindle shaped-sclerites cemented by crystallites. The elemental composition of the sclerites differed from that of the cementing crystallites, in featuring ~8% Mg in the former and none in the latter. Inductively coupled plasma mass spectrometry revealed fragments of spiculite to be composed of 35% sclerites and 65% crystallites. X-ray powder diffraction analysis of individual sclerites indicated that they are composed exclusively of magnesium-calcite, and the spiculite fragments to also feature 9.3 ± 4% aragonite and 5-7% amorphous calcium carbonate. Consequently, it is proposed that the formation of the crystallites, which lithify the sclerites, is caused by a non-biogenic aragonite precipitation, and that the living colony might benefit from this protruding spiculite structure by means of enhanced exposure to water flow.

Search for mesophotic octocorals (Cnidaria, Anthozoa) and their phylogeny. II. A new zooxanthellate species from Eilat, northern Red Sea.

An octocoral survey conducted in the mesophotic coral ecosystem (MCE) of Eilat (Gulf of Aqaba, northern Red Sea) yielded a new species of the speciose reef-dwelling genus Sinularia. It features encrusting colony morphology with a thin, funnel-shaped polypary. Sinularia mesophoticasp. n. (family Alcyoniidae) is described and compared to the other congeners with similar morphology. Both the morphological and molecular examination justified the establishment of the new species, also assigning it to a new genetic clade within Sinularia. The results highlight its unique phylogenetic position within the genus, and this is the first described species of a mesophotic zooxanthellate octocoral.

Search for mesophotic octocorals (Cnidaria, Anthozoa) and their phylogeny: I. A new sclerite-free genus from Eilat, northern Red Sea.

This communication describes a new octocoral, Altumia delicatagen. n. & sp. n. (Octocorallia: Clavulariidae), from mesophotic reefs of Eilat (northern Gulf of Aqaba, Red Sea). This species lives on dead antipatharian colonies and on artificial substrates. It has been recorded from deeper than 60 m down to 140 m and is thus considered to be a lower mesophotic octocoral. It has no sclerites and features no symbiotic zooxanthellae. The new genus is compared to other known sclerite-free octocorals. Molecular phylogenetic analyses place it in a clade with members of families Clavulariidae and Acanthoaxiidae, and for now we assign it to the former, based on colony morphology. The polyphyletic family Clavulariidae is, however, in need of a thorough revision once the morphological distinctions among its phylogenetically distinct clades are better understood.